Biological, biochemical and molecular aspects of diabetogenic and nondiabetogenic variants of encephalomyocarditis (EMC) virus are being studied in vitro and in animal model systems. The identification of genetic differences between these variants and molecular mechanisms involved in the pathogenesis of diabetes mellitus are under current investigations. The interaction between various environmental agents, namely viruses and chemicals or among viruses themselves in the pathogenesis of diabetes and long-term complications in animals also has been investigated. The role of the humoral immune system in the pathogenesis of insulin-dependent diabetes mellitus has been studied. This included the identification of autoantibodies to intracellular components and cell membrane antigens of islet cells. These studies were directed to elucidate the role played by these autoantibodies in the pathogenesis of insulin-dependent diabetes mellitus. Studies to understand the machanisms involved in virus-induced autoimmunity also are in progress.